[FIXED JENKINS-20276] Use a patched version of jnr-ffi

While we await the merge of https://github.com/jnr/jnr-ffi/pull/23
[maven-release-plugin] prepare release ssh-agent-1.4.2
[maven-release-plugin] prepare for next development iteration
Merge branch 'temp'
Add support for multiple credentials (subject to JENKINS-23160 until we upgrade the credentials plugin dependency)
Fix javadoc